The principal target cells of in vivo HIV infection are the CD4-positive T-cells and cells of the monocyte lineage. However, little is known about the role of other phagocytic cells (i.e. neutrophils) in AIDS. The neutrophil is a primary cellular component of host defense against bacterial infection (e.g. periodontal disease) and neutrophil dysfunction does occur in AIDS. The goal of this study was to examine the biological properties of the neutrophil-precursor HL-60 cell line after infection with HIV-1. To accomplish this, a chronically infected HL-60 culture was established using the HIIV-IIIb isolate. Productive infection with HIV was measured using a HeLa-CD4-ltr-beta gal indicator (MAGI) cell assay system and p24 production. Analysis of the infected HL-60 culture revealed that only 25% of the cells were infectious. Immunofluorescence (IF) studies suggested the presence of HIV proteins in about 50% of cells in this culture. Limiting dilution allowed for further isolation of two HIV-infected HL-60 subclones (see Table). Subclone #1 displayed a high level of infection by IF, but did not produce infectious virus. Subclone #22, as confirmed by methods of detection, appeared to be nearly 100% infected and capable of production/transmission of infectious HIV particles. Electron microscopy was used to show the presence of intact HIV particles. In situ hybridization (ISH) studies, using HIV-specific digoxigenin-labeled RNA probes, demonstrated high levels of viral mRNA intracellularly in the "parent' as well as in the two subclones. Culture MAGI%* p24(ug/ml)* IF(%)* ISH(%)* parent HL-60 25 138 50 60 subclone #1 0 127 90 60 subclone#22 100 400 95 100 *percentage of total cells estimated to be position. In conclusion, subclones #1 and #22 may serve as useful in vitro analogues for the study of the altered phagocytic response in the HIV-infected host. The establishment of the parameters concerning the HIV infection of this promyeloctic cell line may provide new knowledge into the cellular mechanisms of HIV pathogenesis in the host. Key words: HIV infection, HIV pathogenesis, HL-60, neutrophils, phagocytes